+static struct commit *check_commit(struct object *obj, unsigned char *sha1)
+{
+ if (obj->type != commit_type) {
+ error("Object %s is a %s, not a commit",
+ sha1_to_hex(sha1), obj->type);
+ return NULL;
+ }
+ return (struct commit *) obj;
+}
+
+struct commit *lookup_commit_reference(unsigned char *sha1)
+{
+ struct object *obj = parse_object(sha1);
+
+ if (!obj)
+ return NULL;
+ if (obj->type == tag_type)
+ obj = ((struct tag *)obj)->tagged;
+ return check_commit(obj, sha1);
+}
+